This invention relates to bulkable polyester textile yarns, and more particularly to mixed-shrinkage yarn composed of an intimate mixture of polyester filaments of different chemical composition.
Mixed-shrinkage yarns are composed of low-shrinkage filaments and higher-shrinkage filaments. They can comprise polyethylene terephthalate filaments which have been produced under different conditions and then combined by twist-plying or jet-interlacing as disclosed in Maerov et al. U.S. Pat. No. 3,199,281. When the filaments are heat-shrunk, the higher-shrinking filaments pull the other filaments into a bulky configuration. A mixed-shrinkage yarn has been obtained by simultaneously melt-spinning polyethylene terephthalate filaments, one yarn bundle of low relative viscosity and the other of higher relative viscosity, quenching them differently, combining the two bundles of filaments into a composite yarn, and then drawing and heat-setting the filaments under the same conditions, as disclosed in my U.S. Pat. No. 3,444,681. A mixed-shrinkage yarn is obtained because the two types of filaments respond differently to the drawing and heat-setting treatments.